In many environments, monitoring of telephony calls to detect and/or prevent unauthorized activities is desirable. For example, private premise-based telephone systems, such as those installed at correctional facilities or other controlled-environment facilities, generally desire to monitor various events occurring on the telephone lines of the system. Telephone systems at correctional facilities or other controlled-environment facilities may comprise a microprocessor-based call processing system having operational software that is capable of allowing control over telephones connected to the system. For example, the system may be programmed to prevent residents (e.g., inmates of a correctional facility) from contacting unauthorized parties or using the telephone system for fraudulent purposes. An authorization mechanism may be utilized to prevent residents from dialing unauthorized numbers directly. For instance, in a correctional facility, such as a prison, a call processing system may be employed for preventing an inmate from calling certain unauthorized parties as judges, a victim of the inmate's crime and/or family members of the victim, and known crime associates of the inmate, as examples.
Additionally, a call processing system my prevent a resident from initiating a three-way call, taking part in a conference call, or the like. However, a particular problem that is encountered in these systems is the placement of a three-way call, or the like, by a party that is authorized to be called by the resident. Once the resident is connected to an authorized number, the resident may be connected to a third party at an unauthorized number via the three-way call feature by a party at the authorized number. Care may be taken to insure that a resident does not call an unauthorized party. However, once a call is connected through the Public Switched Telephone Network (PSTN) it becomes very difficult to control the actions of the called party. Therefore, to preserve this screening activity, it is often desirable to insure that the called party is in fact the person to whom the call is terminating. Therefore, it is often desirable to have control of the call with respect to all the parties who are on the phone call. In short, it is desirable to prevent addition of an unknown third party to a resident call in order to preserve the integrity of the initial call screening.
A three-way call may be initiated when the originally called party (e.g. an authorized party outside the private telephone system) depresses the hook switch on the telephone, generating a hook flash signal. This signals the telephone central office to put the resident on hold and provide a dial tone to the originally called party. On receipt of the dial tone, the originally-called party dials the number of an unauthorized third party, and when the connection is completed, the resident and the unauthorized third party can communicate through the connection established outside the private system.
Three-way call monitoring systems which have been developed to prevent unauthorized calls according to the foregoing scenario rely on the detection of telephone signals. They typically monitor the local telephone connection for the hook flash “click” signal or associated central office signals that fall in a frequency band outside the range of frequencies produced by the human voice. These systems typically monitor signals on the local telephone line through a frequency filter designed to pass audio signals in this frequency band. A three-way call attempt may be indicated whenever signals in the frequency band have energies above a selected threshold. Some systems compare the signals with a hook flash reference signal utilizing sampling techniques implemented with a digital signal processor (DSP).
Even in a more or less conventional telephone environment these systems may not be very accurate for a number of reasons. The underlying assumptions about the frequency profile of three-way call events, i.e. the hook flash and signals generated by activating central office switches, are often wrong. For example, the hook flash signals are often modified by transmission through switches and along loaded lines, and even if assumptions about the frequency characteristics of the initial signal are accurate, these characteristics may be substantially distorted by the time the “hook flash” signal reaches a call processing system implementing three-way call detection, or the like.
Other systems and methods for detecting undesired call activity are disclosed in Salibrici, U.S. Pat. No. 5,768,355 and above-incorporated commonly owned, co-pending U.S. patent application Ser. No. 10/252,956, filed Sep. 20, 2002 and titled THREE-WAY TELEPHONE CALL PREVENTION SYSTEM AND METHOD. Salibrici teaches using digital signal processing to identify a third-party connection. Salibrici operates by establishing a baseline ambient, or background, noise level, and detecting when the signal noise level drops below the ambient noise level. When the current signal noise level drops below the ambient noise level, the system assumes that a three-way conference call has been attempted by the called party. U.S. patent application Ser. No. 10/252,956 discloses an exemplary technique for detecting three-way calls, which in general includes detecting a call signal level, determining if the call signal level is below a predetermined silence level threshold, and measuring a duration the call signal level remains below the predetermined silence level threshold.
Certain calls may have their audio carried over at least a portion of a communication network as packets. For example, Voice over IP (“VoIP”) is one example in which at least a portion of a call's is carried as packets over a communication network. Internet protocol (“IP”) is a routing protocol designed to route traffic within a network or between networks. VoIP is a known method for providing voice capabilities over an IP network, such as the Internet or an intranet. In such networks data packets are sent to and from communication sites to facilitate communication. In communication systems utilizing a VoIP protocol, the packets are commonly referred to as datagrams. In typical VoIP networks, each communication site sends datagrams to other communication sites with which they are in communication. There are different approaches to sending datagrams. Control signals per ITU recommendation H.323, and audio-based media streams using Real-Time Transport Protocol (RTP) per Internet RFC 1889, may be applied. Alternatively, control signals could be applied using other protocols such as Session Initiation Protocol (SIP) per Internet RFC 2543.
Potentially even more difficult to detect than a three-way call is a handoff of a call from an authorized party to an unauthorized party. For instance, a resident may call an authorized party's number and the authorized party may even initially answer the call; however, after the call is authorized by the call processing system (e.g., after the system verifies that the resident is authorized to speak with the called party), the called party may, during the course of the ongoing call, hand off the telephone to another party (or place the call on speaker phone so that another party can participate in the call). Similarly, after a call is authorized and connected for the resident, the resident may hand off the call to another resident who is not authorized to participate on the call. In this manner, a called party and/or a resident may facilitate an unauthorized party to participate on a call after the call is initially authorized for the resident and called party. With such a handoff, no indication of the handoff is available in the call's signaling, as with the hook flash signal that may be used in traditional PSTN calls for detecting three-way calling attempts.
In view of the above, a desire exists for monitoring calls for detecting and/or preventing unauthorized activity during the calls, such as detecting a call to an unauthorized party, detecting an unauthorized three-way call, etc. As mentioned above, detecting certain unauthorized activity, such as an unauthorized three-way call, is particularly problematic when the call is carried via packets, as in VoIP.
Also known in the art is the use of various biometric data for identifying individuals (e.g., for investigative purposes, for restricting access to particular areas of a building, etc.). For instance, fingerprinting technology is well-known for identifying, with some degree of confidence, an individual based on a fingerprint. Indeed, an individual may be identified with a high-level of confidence based only on a partial fingerprint, if a sufficient number of characteristic points are available on the partial fingerprint. Various other biometric identification of humans that are known in the art include face recognition, voice recognition, iris scanning, retina imaging, and handwriting analysis. Various computer-executable processes for performing such biometric identification are known in the art.
Certain voice recognition techniques have been proposed for identifying parties to a telephony call. As one example, U.S. Pat. No. 6,246,751 (“the '751 patent”) issued Jun. 12, 2001 describes a technique for identifying a caller to prevent unauthorized call forwarding. In the '751 patent, speech is captured from a caller attempting to place a call, and the speech is used to identify the caller to detect and prevent fraudulent use of call forwarding.
As another example, U.S. Pat. No. 5,170,426 (“the '426 patent”) issued Dec. 8, 1992 discloses a method and system for home incarceration. According to the '426 patent, monitoring and verification is performed through a telephone network including a telephone on the premises of the location of confinement and a control center. Voice verification, using voice analysis of speech transmitted in a telephone call from the site to the center is performed. A voice template vocabulary is established for the individual and used for voice verification. Caller line identification of each incoming call is performed to verify that call originates from the appropriate location. The confined individual is required, either randomly or at scheduled intervals, to call the control center and recite a statement including randomly selected words from the template vocabulary. This enables the system to verify that the caller is indeed the confined person and is calling from an appropriate location to which he is to be confined.
Similarly, U.S. Pat. No. 6,101,242 (“the '242 patent”) discloses method and system for home incarceration. According to the '242 patent, voice identification is used to identify a caller and an answering party. A corresponding profile of one or more of the identified parties may then be used for the call. The profile may specify, for example, particular keywords to be detected during the call, a particular billing arrangement to be imposed for the call, etc.
As yet another example, U.S. Pat. No. 4,843,377 (“the '377 patent”) discloses an arrangement for home incarceration which proposes the use of a voiceprint as a means for remote prisoner identification. In the '377 patent, audio spectral analysis is performed and applied to speech transmitted over a telephone line to determine a match with a probationer's voiceprint.